Cast rotor and method



March 1957 w. H. GUNSELMAN 2,784,333

CAST ROTOR AND METHOD Filed Aug. 5, 1953 IN VEN TOR. WAYNE H. GUN SELMAN March 5, 1957 w. H. GUNSELMAN 2,784,333 CAST ROTOR AND METHOD FiledAug. 3, 1953 2 Sheets-Sheet 2 INVENTOR. WAYNE H. GUNSELMAN BY UnitedStates Pater-i 2,784,333 iatented Mar. 5, 1957 CAST ROTOR AND METHOD-Wayne H. Gunselman, Cleveland, Ohio, assignor to Reliance Electric andEngineering Company Application August 3, 1953, SerialNo. 372,123 6Claims. (Cl. 310-211) The invention relates in general to castingmethods and moreparticularly to a means for permanent mold casting theend. rings for a squirrel cage induction motor rotor for use in highslip, high torque, and excessive mechanical abuse. applications.

Pressure-die casting has been used for many years to 2 form theconductor system for a squirrel cage induction motor rotor. The metalsgenerally used in such die casting operations were alloys, principallyaluminum and magnesium alloys. Such alloys require a temperature of onethousand to one thousand two hundred degrees Fahrenheit to besufliciently molten to be pressure die cast. The melting temperaturemight be about nine hundred degrees, and this temperature wassufiiciently low that if the motor was heavily abused, such as highfrequency of starts and stops, the electrical losses in the rotor wouldbecome so great as to melt the squirrel cage conductor system. In atypical prior art system of pressure die casting the molten metal wasplaced in a die casting pot which was lined with asbestos and mica, andthese two materials were also used in the dies as a seal. For a typicallarge sized rotor approximately five hundred pounds of aluminum alloywould be melted and in the die casting pot. Approximately one hundredfifty pounds of the alloy would be shot under pressure to form theconductor bars and end rings of the squirrel cage conductor system. Thismeant that three hundred fifty pounds of the alloy was wasted because itwas mixed with particles of asbestos and mica so that it was notreclaimable.

An object of the invention is to cast the short circuit ing endrings ona squirrel cage rotor and to effect a satisfactory electrical andmechanical bond with separately permanently molded conductor bars in theslots of the rotor.

Another object of the invention is to provide a rotor of high mechanicalstrength and rigidity.

Another object of the invention is to provide a squirrel cage rotorhaving a conductor system made of high meltingpoint alloy which willwithstand the internal heat created by excessive starting and stoppingof the motor underload.

Another object of the invention is to provide a squirrel cage rotorconductor system permanently molded from an alloy which cannotsuccessfully be die cast because of excessive temperatures which woulddamage the rotor laminations. {)0

Another object of the invention is to provide a method of makingsquirrel cage conductor systems wherein the molten metal not actuallyused in forming the conductor bars and end rings may readily bereclaimed.

Another object of the invention is to provide a squirrel cage conductorsystem on an induction motor rotor wherein the rotor does not have anyappreciable residual stresses resulting from improper directionalsolidification and/ or non-uniform shrinkage.

Another object of the invention is to provide a squirrel 7 cage rotorwhich is more tightly compressed at the periphery than near the centerthereof.

Other objects and a fuller understanding of this invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

Figure 1 shows a three-dimensional view of a separately cast conductorbar;

Figure 2 shows a perspective view of a combined press and mold formaking a-squirrel cage rotor;

Figure 3 is a view of the rotor laminations;

Figure 4'isathree-dimensional view of the rotor after the end rings arecast and with one pair of gates and risers trimmed off;

Figure 5 is a partial longitudinal sectional view through the completedrotor; and

Figure 6 is an enlarged partial sectional view of a modification.

The aluminum and magnesium alloys previously used in many die castrotors would melt at about nine hundred degrees, and this wassufiiciently low that several squirrel cage conductor systems meltedunder operating conditions which were such as to cause heavy electricallosses in the motor. A higher melting point alloy thus became necessary.An aluminum bronze alloy containing about ninety percent copper, ninepercent aluminum, five-tenths percent nickel, and a small quantity ofiron is found to have a high melting point of about one thousand ninehundred ten to one thousand nine hundred sixty degrees Fahrenheit, andyet have the same resistance required for this high slip motor of tenpercent or more slip. This alloy had the required high melting point forsuch abusive operating conditions but was found to be impossible to diecast. The laminations of the rotor have thereon an insulating film toprevent eddy current losses, and this insulating film would withstand atemperature of only about three hundred fifty degrees. To die castaluminum bronze at the high temperature required in the order of twothousand two hundred degrees Fahrenheit would require that the rotor bepreheated so that the molten metal even under pressure could be forcedcompletely through the slots before it solidified. Such preheating ofthe rotor would have to be at temperatures of about one thousanddegrees, and this was impractical because not only would the laminationinsulation be burned off but the laminations themselves would bedamaged. Further, the insulation around the openings of the dies wouldnot withstand the temperature and pressure.

The present invention relates to a method of separately casting theconductor bars, placing them through the slots of the rotor, and thencasting by a permanent mold process end rings in electrical andmechanical contact with the ends of the conductor bars.

The Figure 1 shows a conductor bar 11 separately cast by a permanentmold process. Permanent molding is differentiated from die casting inthat the metal to be cast is poured by gravity flow into a mold ratherthan being forced thereinto by pressure. The conductor bars 11 haveexposed ends 12 each of which has mechanical locking grooves 13 and aplurality of serrations 14. The serrations 14 are preferably sharp toestablish a fusible surface. The bars 11 may have slightly curvedsurfaces 15 and 16 in order to facilitate their removal from the mold inwhich cast.

The Figure 3 shows a plan view of a rotor lamination 19 having aplurality of slots 20. These slots may be either open or closed inaccordance with usual practices. A keyway 21 may be incorporated in eachof the laminations 19.

The Figure 5 shows the completed squirrel cage rotor 22 and shows that aplurality of laminations 19 are stacked on a spider 2 3. The spider is aheavily constructed weldment including a tubular center 24 and arms 25welded thereto. This construction is better shown in Figure 4. Thelaminations 19 are placed on the spider 23 in groups 26, there beingfour such groups in the particular rotor shown. Ventilating air spaces27 are provided between the groups 26. Spacer fingers 28 in the airspaces 27, which may be disposed generally radially, maintain the groups26 separated. One of the spider arms may contain a keyway 29 with a key30 placed therein and engaging the keyway 21 on the laminations Y 19.Such keyway 2? may be skewed if desired in accordance with conventionalpractices. The groups of laminations 26 and spacer fingers 28 areassembled on the spider 23 with this assembly then placed in a pressmold 31, shown in Figure 2. This press mold 31 is a horizontal presshaving an end frame 32 at the right end and'a similar end frame at theleft end, not shown. Strain rods 33 hold together the end frames. Amovable head 34 slides on the strain rods 33 and is actuated by a pressure source such as a fiuid motor, not shown, at least before moldingthe last to be molded of the two end rings. A three-part mold,comprising mold parts 35, 36, and 37, is provided near the end frame 32.A similar three-part mold, including the mold part 38 and two otherparts not shown, is provided on the movable head 34. Each three-partmold together with a rotor in place defines an end ring cavity, shownprincipally at 39, for casting the end rings 46, shown in Figure 5. Themold parts 35 and 36 are mounted on a pivot 41 and are shown in an openposition. Pneumatic motors 42 and 43 open and close the mold parts 35and 36. The outer edge 44 of the end faces of the stack of rotorlaminations engages the annular edge 45 of the mold part 37. The moldpart 37 also includes an annular ring 46 which closely encompasses thespider 23 and abuts the major portion 47 of the end laminationson therotor. Tongues 48 on the mold part 37 establish a plurality of gates 49through which the molten metal may flow to the end ring cavity 39. Ariser cavity 50 is provided in the mold part 37, and this riser cavityhas a top opening 51. A blind riser .52 and air vent 54 are alsoprovided in the mold part 37. A conical centering member 53 is alsofixed relative to the mold part 37 and engages and centers the end ofthe tubular center 24 of the spider 23.

Before permanent molding of the end rings 49 annular spacer strips, notshown, may be temporarily placed in the ventilating air spaces 27 andtack welded in place to aid the spacer fingers 28 in maintainingparallelism of the laminations 19. The press mold 31 includes gas lines56 leading to burners, not shown, on the outside of the mold, forpreheating the mold parts 35 to 38 to approximately seven hundred tonine hundred degrees Fahrenheit. This heat will also preheat the rotorwhen placed in the mold to about three hundred degrees Fahrenheit.

The exposed ends 12 of the conductor bars are preferably tinned withsilver solder and then coated with flux and inserted through the slotsof the stacked rotor laminations. The spider 23 with the groups 26 ofrotor laminations with the conductor bars 11 in place may then be placedin the press mold 31. The movable head 34 may then be moved forward onthe strain rods 33 by the motor of the press mold. The annular ring 46,and a similar ring on the head 34 will therefore contact the endlaminations of the rotor to greatly compress the rotor laminations. Themold parts 35 and 36 and the similar mold parts on the other end ringmay then be closed to form the end ring cavities. The aluminum bronzealloy is then ready to be poured into the top openings 51. The aluminumbronze alloy is heated to a temperature of about two thousand twohundred fifty degrees and the pouring crucibles are preheated to preventchilling of the metal in the pouring crucibles. The pouringtempera-'ture is approximately two thousand one hundredto two thousand twohundred degrees Fahrenheit and iskept generally at a low temperaturerelative to the melting temperature of the alloy so as not to causeburning out or thirds the depth of the end rings.

oxidation of the alloy elements such as aluminum and nickel during thepouring operation. The riser cavities 50 and gates 49 are made of amplecapacity so that the entire pouring operation may be rapidly completedand the end rings 46 completely cast before solidification. In thepresent case rotors actually cast are thirty inches diameter and theforce of the press is one hundred twenty tons, with about two hundredseventy-five pounds of aluminum bronze alloy being melted for each rotorwith the end rings weighing approximately one hundred seventy-fivepounds and the remaining one hundred pounds being in the gates andrisers which is immediately reusable and reclaimable since it containsno contaminants.

The temperature of the metal as cast, under the conditions outlinedabove, and the cross-sectional area of the end rings 40 is sufiicient tocause a satisfactory electrical bond with the exposed ends 12 of theconductor bars 11, especially at the sharp edges of the serrations 14.The molten metal of the end rings flows around the exposed ends 12 andforms good mechanical interlocking engagement with the mechanicallocking grooves 13. Thus, a good mechanical bond is achieved at thelocking grooves 13 and a good electrical bond is achieved at theserrations 14. V

A fusion between the conductor bars and the end rings is not absolutelynecessary, as evidenced by the usual bus bar construction andthe type ofcontact made in electrical switches. What is desired is a satisfactoryelectrical bond or connection between the end of the conductor bars andthe end ring. To determine if there is a satisfactory electrical bond,the motor is repeatedly tested under full load locked rotor conditions,creating repeated heating and cooling cycles. Such satisfactoryelectrical bond is demonstrated by the fact the the amount of slip ofthe motor before and after such testing cycles is essentially the same.This shows that the electrical bond is tight enough so that repeatedheating and cooling, with consequent expansion and contraction, will notcreate oxidation at the joint which will change the resistance of thisjoint. The exposed ends of the conductor bars 12 have been shown as andare preferably about two- The conductor bars as previously permanentlymolded have cross-sectional dimensions approximately .010 inch less thanthe crosssectional dimensions of the slot apertures. This assures thatthe bars will be able to slide through the slot apertures.

After solidification of the end rings the mold may be opened and thepress pressure released and the rotor removed. Upon releasing thepressure of the press mold 31, the conductor bars 11 will be placedunder tension, in this case approximately six to seven thousand poundsper square inch on each conductor bar. The aluminum bronze alloy has atensile strength many times this figure; hence, it will retain the outerperiphery of the stack laminations in a tightly compressed condition.The annular spacer rings in the ventilating air spaces 27.may then beremoved since they have served their purpose of assuring parallelism ofthe laminations 19, and in practice the annular spacer rings mayconveniently be removed during the machining operation which makes theouter diameter of the rotor cylindrical. Thus these spacer rings do notappear in the completed rotor view of Figure 5. The gates and risers maynext be trimmed off and are immediately reusable. The Figure 4 shows oneend ring 46 after being trimmed and with the far end ring stillretaining the gates 57 and risers 58. To complete the rotor, annular endplates 59 are pressed up against the end faces of the rotorand weldedthereto as shown at 60. This last-mentioned compressional force ispreferably not nearly as great as the pressure originally used tolongitudinally compress the rotor. 'It may be only a force sufficient tomake sure that the end plates 59 are in intimate contact with the endfaces of the rotor before welding thereto. This will establish thatutheouter periphery of the rotor is compressed more than the portion of therotor next to the spider 23. Next, these end plates and the end group oflaminations may be drilled and tapped, and cap screws 61 screwed thereinwith the cap screws welded at 62 to the end plates 59. This makes amechanically rigid structure which will stand extreme abuse, bothmechanical and electrical.

The annular spacer rings temporarily used at the periphery of the airspaces 27, plus the fact that the conductor bars 11 are previously castand in a solid state at the time of casting the end rings on a rotortightly compressed, establishes a completed rotor wherein thelaminations do not have any waviness since there is no non-uniformshrinkage of the conductor bars as in die cast rotors.

The Figure 6 shows a modified form of construction forachieving amechanical and electrical bond. In this Figure 6 a conductor bar 65 hasa modified form of exposed end 66. In this form there is only onemechanical locking groove 13 which is positioned on the side closest tothe axis of the rotor. The side 67 of the exposed end 66 remote from theaxis of the rotor is left generally straight. The serrations 14 may beretained. In this modification the exposed ends 66 do not need to betinned and fiuxed. The bars 65 are inserted through the slots in therotor so that the exposed ends 66 are symmetrical on each end of therotor. The rotor with the bars in place is then placed in the press mold31 as before, and the end rings 69 cast in place. After the rotor isremoved fromthe press mold, a peripheral groove 68 is machined in theouter periphery of the end ring 69. This groove 68 is made deep enoughto cut into each of the sides 67 of the bars 65. i The rotor is thenplaced in a welding machine, such as an inert gas welder, and thegrooves 68 filled up with weld metal 70 which is preferably of the samecomposition as the aluminum bronze used in the bars 65 andend rings 69.The weld metal 70 therefore assures a complete electrical bond betweenthe bars 65. and the end rings 69. It also, in combination with thelocking groove 13 and serrations 14, will provide mechanical lockingengagement therebetween. The complete squirrel cage rotor 22 may becompleted by the welding on of the end plate 59 and cap screws 61 asbefore.

With either of the constructions. shown in Figures 5m 6 an advantage ofthe present invention is that the entire rotor need not be scrapped whenthere is an imperfect casting as was the case in the pressure diecasting of the squirrel cage structure. In this invention the rotorlaminations may be salvaged since in the event of an imperfect end ringcasting, such end rings may be cut off, the conductor bars slid out ofthe slots, and thus the rotor laminations may be salvaged for reuse.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement or parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. The method of making a squirrel cage conductor structure for alaminated member having longitudinal slots, said method comprising,forming separate conductor bars for said slots having a length longerthan said rotor, inserting a bar in each of said slots substantiallylongitudinally symmetrically to establish exposed portions at each endthereof, molding by a permanent molding process first and second endrings on the end faces of said rotor and with said bar end portionsembedded in said end rings, cutting a peripheral groove in said endrings to a depth sufificient to cut into said bar exposed portions, andfilling said groove with weld metal to establish electrical andmechanical interconnection of said bars and end rings.

2. A squirrel cage conductor structure for an alternating currentinduction motor laminated member having longitudinal slots around theperiphery thereof, comprising separately cast conductor bars havingcross-sectional dimensionsapproximately .010 of an inch undersize of theslots in said member, said bars having a length greater than that of themember to establish two exposed ends outboard of the faces of themember, a mechanical locking groove on each exposed end of said bars,sharp fusible protrusions on each exposed end of said bars, and firstand second annular end rings in contact with the longitudinal ends ofsaid member joining opposite exposed ends of said bars, said end ringsand bars being formed of aluminum bronze consisting of approximatelyninety percent copper, nine percent aluminum, five-tenths percentnickel, and a small quantity of iron, said end rings being cast at atemperature and with a cross-sectional area sufiicient to transfer aquantity of heat to the end portions of the bars to cause a satisfactoryelectrical bond between said end rings and bars especially at saidprotrusions and with mechanical interlocking engagement between saidlocking grooves and said end rings, said laminated member having thegreatest compression at said periphery, peripheral grooves cut into saidend rings to a depth sufficient to cut into said bar exposed ends, andweld metal filling said peripheral grooves and establishing electricaland mechanical interconnection of said bars and end rings.

3..A squirrel cage conductor rotor structure for an alternating currentinduction motor laminated rotor having longitudinal slots around theperiphery thereof, comprising separately cast rotor bars havingcross-sectional dimensions approximately .010 of an inch undersize ofthe slots in said rotor, said bars in cross-section having at least twogenerally opposite sides at least slightly curved,said bars having alength greater than that of the rotor to establish two exposed endsoutboard of the faces of the rotor, first and second generally oppositedeep locking grooves on each exposed end of said bars, each exposed endof said bars having sharp serrations thereon, said exposed ends beingtinned with silver solder and coated with flux, and first and secondannular end rings in contact with said rotor faces joining oppositeexposed ends of said bars, said end rings and bars being formed ofaluminum bronze consisting of approximately ninety percent copper, ninepercent aluminum, five-tenths percent nickel, and a small quantity ofiron, said end rings being cast at a temperature of approximately twothou sand one hundred degrees Fahrenheit by a permanent mold processwith the cross-sectional area of the end rings being sufiicient totransfer a quantity of heat to the end portions of the bars to cause asatisfactory electrical bond between said end rings and bars especiallyat said serrations with the exposed ends of the bars embedded in the endrings approximately two-thirds of the depth of the end rings and inmechanical interlocking engagement with said deep grooves, saidpermanent mold casting being accomplished during longitudinalcompression of said rotor to thus place the rotor bars in the com pletedrotor under a tensile force of approximately seven thousand pounds persquare inch to thus accomplish greater longitudinal compression near theperiphery of the rotor than near the center of the rotor.

4. A squirrel cage conductor rotor structure for an alternating currentinduction motor laminated rotor having longitudinal slots around theperiphery thereof, comprising separateiy cast rotor bars havingcross-sectional dimensions slightly undersize of the slots in saidrotor, said bars having a length greater than that of the rotor toestablish two exposed ends outboard of the faces of the rotor, a deeplocking groove on each exposed and of said bars, each exposed end ofsaid bars having sharp serrations thereon, and first and second annularend rings in contact with said rotor faces joining opposite exposed endsof said bars, said end rings and bars being 5 formed of aluminum bronzeconsisting of approximately rings being cast at a temperature ofapproximately two 7 thousand one hundred degrees Fahrenheit with thecrosssectional area of the end rings being sufiicient to transfer aquantity of heat to the end portions of the bars to cause a satisfactoryelectrical bond between said end rings and bars especially at saidserrations with the exposed ends of the bars embedded in the end ringsand in mechanical interlocking engagement with said deep groove, saidcasting being accomplished during longitudinal compression of said rotorto thus place the rotor bars in the completed rotor under a tensileforce of approximately seven thousand pounds per square inch to thusaccomplish greater longitudinal compression near the periphery of therotor than near the center of the rotor, peripheral grooves cut intosaid end rings to a depth suflicient to cut into said bar exposed ends,and weld metal filling said peripheral grooves and establishingelectrical and mechanical interconnection of said bars and end rings.

5. A squirrel cage conductor rotor structure for an alternating currentinduction motor laminated rotor hav-- ing longitudinal slots around theperiphery thereof, comprising separately cast rotor bars havingcross-sectional dimensions approximately .010 of an inch undersize ofthe slots in said rotor, said bars in cross-section having at least twogenerally opposite sides at least slightly curved, said bars having alength greater than that of the rotor to establish two exposed endsoutboard of the faces of the rotor, a deep locking groove on eachexposed end of said bars, each exposed end of said bars having sharpserrations thereon, and first and second annular end rings in contactwith said rotor faces joining opposite exposed ends of said bars, saidend rings and bars being formed of aluminum bronze consisting ofapproximately ninety percent copper, nine percent aluminum, five-tenthspercent nickel, and a small quantity of iron, said end rings' being castat a temperature of approximately two thousand one hundred degreesFahrenheit by a permanent mold process with the cross-sectional area ofthe end rings being sutficient to transfer a quantity of heat to the endportions of the bars to cause a satisfactory electrical bond betweensaid end rings and bars especially at said serrations with the exposedends of the bars embedded jin the end rings approximately two-thirds ofthe depth of the end rings and in mechanical interlocking engagemeritWith said deep groove, said permanent mold casting being accomplishedduring longitudinal compression of said rotor to thus place the rotorbars in the completed rotor under a tensile force of approximately seventhousand pounds per square inch to thus accomplish greater longitudinalcompression near the periphery of the rotor than near the center of therotor.

6. A squirrel cage conductor structure for a laminated member havinglongitudinal slots, said conductor structure comprising a plurality ofseparate conductor bars in said slots each having a length longer thansaid rotor and substantially longitudinally symmetrically placed in saidslots to establish exposed portions at each end of said bars, first andsecond end rings cast on the end faces of the rotor and with said barend portions embedded in said end rings, a peripheral groove cut intosaid end rings to a depth suflicient to cut into said bar exposed 7 endportions, and weld metal filling said groove and establishing electricaland mechanical interconnection of said bars and end rings.

References Cited in the file of this patent UNITED STATES PATENTS558,271 Falk Apr. 14, 1896 1,603,544 Johnson Oct. 19, 1926 1,695,799Daun Dec. 18, 1926 1,719,829 7 Bunker July 9, 1929 1,755,283 Adams Apr.22, 1930 1,777,320 McCollum Oct. 7, 1930 1,807,689 Deputy June 2, 19311,925,052 Larsh Aug. 29, 1933 2,265,243 McCullough et al Dec. 9, 19412,285,811 Gay June 9, 1942 2,326,418 Van Amerongen Aug. 10, 19432,328,788 Deputy Sept. 7, 1943 2,544,671 Grange et al. Mar. 13, 1951FOREIGN PATENTS 47,857 Switzerland June 10, 1909

